Colour pickup tubes and method of manufacturing the same

ABSTRACT

In a colour pickup tube of the class comprising a substrate, an optical colour analyzing filter formed on the substrate, a layer of transparent inorganic substance formed on the filter, and a photoelectric converting element formed on the layer of transparent inorganic substance, the last mentioned layer includes two successive layers of different degree of oxygen deficiency.

United States Patent 1 Nobutoki 1 COLOUR PICKUP TUBES AND METHOD OF MANUFACTURING THE SAME [75] Inventor: Saburo Nobutoki, Mobara, Japan [73] Assignee: Hitachi, Ltd Tokyo, Japan [22] Filed: Sept. 5, 1974 [21] Appl. No.: 503,329

Foreign Application Priority Data Oct. 5, 1973 Japan 48-111445 US. Cl. 204/192; 178/72; 313/371; 313/384; 313/386 int. Cl. C23C 15/00; H011 31/00 Field of Search 204/192; 313/371, 384, 313/386 [56] References Cited UNITED STATES PATENTS 8/1959 Knight 204/192 X 10/1959 Weimer 313/371 12/1959 Tou1on..... 313/371 12/1970 Rigo 204/192 X Dec. 23, 1975 3,607,384 9/1971 Banks 117/215 3,647,663 3/1972 Cunningham et 31...... 204/192 3,761,375 9/1973 Pierce ct 204/192 3,804,738 4/1974 Lechaton 204/192 3,830,717 8/1974 Singer et al 204/192 OTHER PUBLICATIONS Kozuma et 3.1., Some Properties of Silica Film made by RF Glow Discharge Sputtering," Japan J. App. Phys, V01. 9, No. 8, Aug. 1970, pp. 983-991.

Primary Examiner-John H. Mack Assistant Examiner-Aaron Weisstuch Attorney, Agent, or FirmCharles E. Pfund, Esq.

[57] ABSTRACT In a colour pickup tube of the class comprising a substrate, an optical colour analyzing filter formed on the substrate, a layer of transparent inorganic substance formed on the filter, and a photoelectric converting element formed on the layer of transparent inorganic substance, the last mentioned layer includes two successive layers of different degree of oxygen deficiency.

7 Claims, 1 Drawing Figure U.S. Patent Dec. 23, 1975 3,928,160

COLOUR PICKUP TUBES AND METHOD OF MANUFACTURING THE SAME BACKGROUND OF THE INVENTION This invention relates to a colour pickup tubes for use in a colour television transmitter, and more particularly to a colour pickup tube capable of preventing discolouration of the optical colour analyzing filter (hereinafter merely called a stripe filter) utilized in the colour pickup tube and a method of manufacturing the same.

Generally, a colour pickup tube includes a stripe filter disposed at its photoelectric converting member and a transparent electroconductive film is closely deposited on the stripe filter. Further a photoconductive film is deposited on the transparent electroconductive film, thus completing the photoelectric converting element. However, this construction is disadvantageous in that where an interference filter film is used as the stripe filter, the thickness of the stripe filter deposited on a substrate causes irregularities of the transparent electroconductive film and the photoconductive film which are deposited on the stripe filter. As a consequence, there are such defects that the signal generated by the photoelectric converting element varies in accordance with the configurationof the stripe filter and that the projections of the filter are damaged by friction during the course of manufacturing. To eliminate these defects it has been proposed to make fiat the conductive film by embedding such transparent inorganic substance in'the recesses formed between the stripes of the filter as an oxide and glass including borosilicate glass, silicon dioxide and quartz glass. These inorganic substances are filled in the recesses by sputtering technique in an inert gas atmosphere. However, it was found that when an oxide is deposited on the stripe filter, the film of the resulting transparent inorganic substance becomes unstable due to deficiency of oxygen. For example, when silicon dioxide SiO is sputtered in argon atmosphere, the resulting film of the silicon dioxide shows a condition of oxygen deficiency of the order of SiO, to SiO Further, when the stripe filter is formed on the substrate by photoetching technique the resulting stripe filter contains absorbed or adhered photoresist, photoresist removing liquid or other organics, which cannot be removed completely from the substrate. Accordingly, while these foreign substances still remaining if the transparent inorganic film were deposited on the stripe filter, reducing action would occur on the surface of the stripe filter due to said deficient oxygen condition of the transparent inorganic substance and to the energy which is generated.

when the substance impinges upon the stripe filter. a consequence, the stripe filter is discoloured, thus greatly impairing its ability as a filter.

Various methods have been proposed to obviate this defect including a method wherein the so-called four electrode type sputtering process is used for sputtering the inorganic substance at a low temperature thus decreasing the energy at the time of impinging the substance onto the stripe filter and hence decreasing the temperature rise of the substrate sputtered, and a method wherein the sputtering speed is decreased for minimizing the temperature rise of the substrates sputtered. However, these solutions greatly delay the growth of the layer of the transparent inorganic substance. For example, it takes more than several tens SUMMARY OF THE INVENTION Accordingly, it is an object of this invention to provide a novel colour pickup tube including a layer of transparent inorganic substance capable of preventing 0 the discolouration of the stripe filter and an improved method of manufacturing such improved colour pickup tube capable of depositing the layer of the transparent inorganic substance in a relatively short sputtering time. According to one aspect of this invention there is provided a colour pickup tube of the class comprising a substrate, an optical colour analyzing filter formed on the substrate, a layer of transparent inorganic substance formed on the optical colour analyzing filter, and a photoelectric converting element including a transparent electroconductive film and a photoconductive film which are successively applied onto the layer of the transparent inorganic substance, characterized in that the layer of the transparent inorganic substance includes two successive layers of different degree of oxygen deficiency and that one layer has a larger thickness than the filter.

According to another aspect of this invention, there is provided a method of manufacturing a colour picture tube of the class wherein an optical colour analyzing filter is formed on a substrate, a layer of transparent inorganic substance is formed on the optical colour analyzing filter, and then a photoelectric converting element is formed by successively applying a transparent electroconductive film and a photoconductive layer upon the ,layer of transparent inorganic substance, characteriied in that a first layer of the transparent inorganic substance is applied upon the filter in a mixed atmosphere of an inert gas and oxygen, and then a second layer of the transparent inorganic substance is applied on the first layer in atmosphere containing a smaller quantity of oxygen than the mixed atmosphere.

According to still further aspect of this invention, the method just described is modified such that the layer of the transparent inorganic substance is formed upon the filter in a mixed atmosphere of an inert gas and oxygen, and that the oxygen content of the mixed atmosphere is reduced gradually thereby gradually varying the degree of oxygen deficiency of the layer from the filter toward the photoelectric converting element. Although the layer of the transparent inorganic substance does not contain any interfere between layers of different degree of oxygen deficiency, the layer as a whole functions in the same manner as the two layers prepared by the first mentioned method and having different degree of oxygen deficiency.

BRIEF DESCRIPTION OF THE DRAWING Further objects and advantages of the invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawing in which a single FIGURE shows a crosssectional view of a portion of the photoelectric converting element of a colour pickup tube embodying the invention. Description of the Preferred Embodiment The photoelectric converting element shown in the accompanying drawing comprises a substrate of an insulator l, a stripe filter 2 deposited on one surface of the substrate, and a layer 3 of transparent inorganic substance made of an oxide, for example silicon dioxide SiO or glass, having a thickness of about from 1 to 5 microns and formed on the upper surface of the stripe filter 2 and an oxygen deficient layer 4 of transparent inorganic substance SiO to Slo having a thickness of from 3 to 50 microns and formed on the surface of the layer of the transparent inorganic substance 3. To form the thinner layers 3 of the transparent inorganic substance on the surface of the stripe filter 2, the first layer 3 is formed by carrying out the low speed sputtering process for a short time so as to avoid the formation of the oxygen deficient condition, or even if such condition is resulted, to make such oxygen deficient condition to be negligibly small, thereby preventing as far as possible the reducing action that might occur between the stripe filter and the transparent inorganic substance, whereas the thicker layer 4 is formed in a short time by high speed sputtering process at the sacrifice of the oxygen deficient condition. In this manner by forming duplicate layers of the transparent inorganic substance the resistance of the stripe filter against discolouration can be greatly improved while at the same time it is not necessary to form the layer of the inorganic substance free from the oxygen deficient condition over a long period thereby saving the cost and time of the manufacturing step. To complete the photoelectric converting element, thereafter a transparent electroconductive film 5 is deposited on the surface of the layer 4 of the inorganic substance by a conventional process and then a photoconductive film 6 is deposited on the transparent conductive film 5.

The method of manufacturing the colour pickup tube of this invention is as follows. More particularly, the interference (dichroic) stripe filter 2 is formed on the substrate 1 by photoetching technique according to the conventional practice. Then a high frequency two electrode type sputtering apparatus filled with a mixture of an inert gas, for example argon, and oxygen is used. in such atmosphere, the layer 3 of the transparent inorganic substance is deposited on the surface of the stripe filter 2 by sputtering for an interval sufficient to grow up the layer 3 to a thickness larger than the thickness of the stripe filter, for example I to 5 microns. Then, after reducing the content of the oxygen in the atmosphere or completely removing the oxygen, the same transparent inorganic material is deposited on the layer 3 to a thickness of 3 to 50 microns, thereby forming the layer 4. The total thickness of the two layers of the transparent inorganic substance is made to be from 3 to 50 microns. Thereafter, as above described the transparent electroconductive film and the photoconductive film are successively formed on the layer 4.

Alternatively, the layer 4 of the transparent inorganic substance may be polished or ground down to a level indicated by a dotted line and then the transparent conductive film and the photoconductive film may be deposited thereon. The thickness of the layers of the transparent inorganic substance is determined depending upon such factors as the configuration of the interference (dichroic) stripe filter, the type of the photoelectric converting element, the desired picture quality, and the design requirement. For example, to obtain a high quality pickup tube having a stripe filter that reflects red and blue lights, it is advantageous to form the layer of the transparent inorganic substance having a thickness of about 40 microns, then polish the surface of the layer to remove the surface irregularity there for reducing the thickness of the layer to about 30 microns.

4 In one embodiment of this invention, a stripe filter 2 was formed on a=substrate I through the well-known prior art technique, thereafter a first transparent sub stance layer of silicon dioxide was deposited on said 5 substrate is the-thickness of about 2 microns in the mixed atmosphere where the pressure thereof was 10' Torr. and the fractional pressure of oxygen gas was l Torr. Hence the fractional pressure of oxygen gas in the mixed atmosphere was reduced to Torr.

9 Then, a second transparent substance layer of silicon dioxide was deposited to the thickness of about 8 microns thereby the total thickness of said first and second layers becoming about 10 microns. The time required for the completion of said layer thickness was about 19 hours. Further the stripe filter made through theabove-mentioned process did not show discolouration anymore.

In the meantime, in accordance with the aforesaid method in which a slower sputtering speed is adapted 20 to avoid the temperature rise of a substrate, it takes 32 As the relatively thin first layer is formed at a low speed and the relatively thick second layer is formed at a high speed it is possible to form the layers of the transparent inorganic substance at substantially the same interval as by the prior art method, and yet it is possible to 35 efficiently prevent discolouration of the stripe filter.

Although silicon dioxide was used as the transparent inorganic substance which was sputtered, any other suitable transparent inorganic substance such as oxide glass including borosilicate glass and quartz glass may be used.

In the foregoing egamples it is possible to stabilize the layer of .the transparent inorganic substance by heating the substrate to a temperature near the softening temperature of glass.

instead of quickly decreasing the oxygen content of the mixture of an inert gas and oxygen, it is also possible to gradually change the composition of the atmosphere mixture by gradually closing the value provided for a pipe for supplying oxygen thereby gradually varying the composition of the transparent inorganic substance. The resulting layer of the inorganic substance does not contain any discrete interface but actually the player functions as if it were composed of two discrete "Mayers of different compositions. Also it may be available that the atmosphere does not contain any of oxygen gas when the second transparent inorganic substance layer is deposited.

In addition to the advantages described above, as the two layers of the transparent inorganic substance can be formed in the same apparatus, it is possible to prevent deposition of dust or forming of scratches.

For this reason, it is possible to produce colour pickup tubes of excellent quality at a high yield.

What is claimed is:

L in amethod of manufacturing a colour pickup tube of the class wherein an optical colour analyzing filter is formed on a substrate, a layer of transparent inorganic substance is formed on said optical colour analyzing filter, and then a photoelectric converting element is formed by successively applying a transparent electroconductive film and a photoconductive film upon said layer of transparent inorganic substance, the improvement which comprises the steps of sputtering a first layer of said transparent inorganic substance upon said filter in a first mixed atmosphere of an inert gas and oxygen, and then sputtering a second layer of said transparent inorganic substance upon said first layer in a mixed atmosphere containing inert gas and a smaller quantity of oxygen than said first mixed atmosphere.

2. The method according to claim l wherein said first layer is formed to have larger thickness than said filter.

3. The method according to claim 1 wherein said first layer is formed at a lower speed sputtering then said second layer is formed by high speed sputtering.

4. The method according to claim 1 wherein after mechanically smoothing the surface of said first layer, said second layer is formed on the smoothed surface.

S. The method according to claim 1 said first layer of said transparent inorganic substance is formed in the mixed atmosphere of an inert gas and oxygen wherein 6 the fractional pressure of oxygen is more than l0 torr.

6. The method according to claim I said second layer of said transparent inorganic substance is formed under the atmosphere wherein the fractional pressure of oxygen is less than 10' torr.

7. In a method of manufacturing a colour pickup tube of the class wherein an optical colour analyzing filter is formed on a substrate, a layer of transparent inorganic substance is formed on said optical colour analyzing filter, and then a photoelectric coverting element is formed by successively applying a transparent electroconductive film and a photoconductive film upon said layer of transparent inorganic substance, the improvement where said layer of transparent inorganic substance is sputtered upon said filter in a mixed atmosphere of an inert gas and oxygen. and the oxygen content of said mixed atmosphere is gradually reduced thereby gradually varying the degree of oxygen deficiency of said layer from said filter toward said photoelectric converting element. 

1. IN A METHOD MANUFACTURING A COLOUR PICKUP TUBE OF THE CLASS WHEREIN AN OPTICAL COLOUR ANALYZING FILTER IS FORMED ON A SUBSTRATE, A LAYER OF TRANSPARENT ING ORGANIC SUBSTANCE IS FORMED ON SAID OPTICAL COLOUR ANALYZING FILTER, AND THEN A PHOTOELECTRIC CONVETING ELEMENT IS FORMED BY SUCCESSIVELY APPLYING A TRANSPARENT ELECTROCONDUCTIVE FILM AND A PHOTOCONDUCTIVE FILM UPON SAID LAYER OF TRANSPARENT INORGANIC SUBSTANCE, THE IMPROVEMENT WHICH COMPRISES THE STEPS OF SPUTTERING A FIRST LAYER OF SAID TRANSPARENT INORGANIC SUBSTANCE UPON SAID FILTER IN A FIRST MIXED ATMOSPHERE OF AN INERT GAS AND OXYGEN, AND THEN SPUTTERING A SECOND LAYER OF SAID TRANSPARENT INORGANC SUBSTANCE UPON SAID FIRST LAYER IN A MIXED ATMOSPHERE CONTANING INERT GAS AND A SMALLER QUANTITY OF OXYGEN THAN SAID FIRST MIXED ATMOSPHERE.
 2. The method according to claim 1 wherein said first layer is formed to have larger thickness than said filter.
 3. The method according to claim 1 wherein said first layer is formed at a lower speed sputtering then said second layer is formed by high speed sputtering.
 4. The method according to claim 1 wherein after mechanically smoothing the surface of said first layer, said second layer is formed on the smoothed surface.
 5. The method according to claim 1 said first layer of said transparent inorganic substance is formed in the mixed atmosphere of an inert gas and oxygen wherein the fractional pressure of oxygen is more than 10 5 torr.
 6. The method according to claim 1 said second layer of said transparent inorganic substance is formed under the atmosphere wherein the fractional pressure of oxygen is less than 10 7 torr.
 7. In a method of manufacturing a colour pickup tube of the class wherein an optical colour analyzing filter is formed on a substrate, a layer of transparent inorganic substance is formed on said optical colour analyzing filter, and then a photoelectric coverting element is formed by successively applying a transparent electroconductive film and a photoconductive film upon said layer of transparent inorganic substance, the improvement where said layer of transparent inorganic substance is sputtered upon said filter in a mixed atmosphere of an inert gas and oxygen, and the oxygen content of said mixed atmosphere is gradually reduced thereby gradually varying the degree of oxygen deficiency of said layer from said filter toward said photoelectric converting element. 